The aggregate pension deficit for the nation’s largest corporations improved in the first quarter, mainly because of the surging stock market this year, according to a recent report from Mercer Investment Consulting.

That aggregate deficit shrank by $185 billion from the end of last year, Mercer says. In March alone, the deficit on an aggregate basis for the Standard & Poor’s 1,500 largest companies fell by $107 billion, Mercer said.

As a result of the deficit shrinkage, the aggregate funded ratio, or the assets divided by liabilities went up to 82 percent compared with 74 percent at the end of 2012, the Mercer report said.

To be fully funded, or holding sufficient funds to pay all retired and yet-to-be retired employees, the ratio should be at 100 percent.

In comparison, the funded ratio for the San Diego County Employees Retirement Association, the $9 billion fund for active and retired county workers, was nearly 79 percent as of June 30, 2012, according to a recent report.

Over at the San Diego City Employees Retirement System, the $6 billion pension fund for San Diego city workers, the funded ratio was 68.5 percent as of mid-2012, according to the pension fund.

— Mike Allen